Method for fabricating semiconductor device

ABSTRACT

A method for fabricating semiconductor device includes forming an etch target layer over a substrate including a cell region and a peripheral region, forming a first mask pattern having a first portion and a second portion over the etch target layer in the cell region and forming a second mask pattern having a first portion and a second portion over the etch target layer in the peripheral region, forming a photoresist pattern over the cell region, trimming the first portion of the second mask pattern, removing the photoresist pattern and the second portion of the first mask pattern and the second portion of the second mask pattern, and etching the etch target layer to form a pattern in the cell region and a pattern in the peripheral region.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present invention claims priority of Korean patent applicationnumber 10-2007-0001061, filed on Jan. 4, 2007, which is incorporated byreference in its entirety.

BACKGROUND OF THE INVENTION

The present invention relates to a method for fabricating asemiconductor device, and more particularly, to a method for forming apattern in a semiconductor device.

When forming a gate pattern in a dynamic random access memory (DRAM), itis often required to further reduce a critical dimension (CD) of aperipheral region to form a high-speed device.

FIGS. 1A and 1B illustrate cross-sectional views of a typical method forforming a semiconductor device.

Referring to FIG. 1A, a polysilicon layer 102 and a nitride-based layer103 for forming a gate hard mask are formed over a substrate 101including a cell region and a peripheral region. Photoresist patterns104A and 104B are formed over the nitride-based layer 103. Thephotoresist pattern 104A is formed in the cell region and thephotoresist pattern 104B is formed in the peripheral region, exposingpattern regions. Hereinafter, the photoresist pattern 104A in the cellregion is referred to as the first photoresist pattern 104A and thephotoresist pattern 104B in the peripheral region is referred to as thesecond photoresist pattern 1043.

Referring to FIG. 1B, the nitride-based layer 103 is etched. Referencenumerals 103A and 103B refer to a first etched nitride-based layer 103Aremaining in the cell region and a second etched nitride-based layer103B remaining in the peripheral region, respectively. In the typicalmethod, at patterns are formed by forming the first and secondphotoresist patterns 104A and 104B exposing the pattern regions in thecell region and the peripheral region and performing the etch processusing the first and second photoresist patterns 104A and 104B.

In the typical method, the first etched nitride-based layer 103A obtainsa vertical profile. In contrast, the second etched nitride-based layer103B obtains a sloped profile as represented with reference denotation‘S’, causing an enlarged CD of the gate pattern in the peripheralregion. The sloped profile is formed because a difference exists inpattern densities between the cell region and the peripheral region, anda loading effect is generated in the peripheral region where a spacingdistance is large between patterns, causing polymers generated whileetching the nitride-based layer 103 to accumulate on sidewalls of thesecond etched nitride-based layer 103B.

CD targets in the cell region and the peripheral region may not both besatisfied because the gate patterns are formed by performing one maskprocess on the cell region and the peripheral region. Also, it may bedifficult to reduce the size below a certain level due to diversepattern forms in the peripheral region.

SUMMARY OF THE INVENTION

Embodiments of the present invention are directed to provide a methodfor fabricating a semiconductor device, which can control criticaldimensions of a cell region and a peripheral region.

In accordance with an aspect of the present invention, there is provideda method for fabricating a semiconductor device, including: forming anetch target layer over a substrate including a cell region and aperipheral region; forming a first mask pattern having a first portionand a second portion over the etch target layer in the cell region andforming a second mask pattern having a first portion and a secondportion over the etch target layer in the peripheral region; forming aphotoresist pattern over the cell region; trimming the first portion ofthe second mask pattern; removing the photoresist pattern and the secondportion of the first mask pattern and the second portion of the secondmask pattern; and etching the etch target layer to form a pattern in thecell region and a pattern in the peripheral region.

In accordance with another aspect of the present invention, there isprovided a method for fabricating a semiconductor device, including:forming an N-type polysilicon layer and a P-type polysilicon layer overa substrate including an N-channel metal-oxide semiconductor (NMOS)region and a P-channel metal-oxide semiconductor (PMOS) region, theN-type polysilicon layer formed in the NMOS region and the P-typepolysilicon layer formed in the PMOS region; forming a metal electrodelayer over the N-type and P-type polysilicon layers; forming a gate hardmask pattern over the metal electrode layer; forming a photoresistpattern exposing the PMOS region; trimming the gate hard mask pattern inthe PMOS region; removing the photoresist pattern; and etching the metalelectrode layer and the N-type and P-type polysilicon layers to formgate patterns using the gate hard mask pattern.

In accordance with still another aspect of the present invention, thereis provided a method for fabricating a semiconductor device, including:forming an N-type polysilicon layer and a P-type polysilicon layer overa substrate including an N-channel metal-oxide semiconductor (NMOS)region and a P-channel metal-oxide semiconductor (PMOS) region, theN-type polysilicon layer formed in the NMOS region and the P-typepolysilicon layer formed in the PMOS region; forming a metal electrodelayer over the N-type and P-type polysilicon layers; forming a gate hardmask over the metal electrode; forming a patterned buffer layer fordefining gate pattern regions over the gate hard mask; forming aphotoresist pattern exposing the PMOS region; trimming the patternedbuffer layer in the PMOS region; removing the photoresist pattern; andetching the metal electrode layer and the N-type and P-type polysiliconlayers to form gate patterns using the patterned buffer layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B illustrate cross-sectional views of a typical method forfabricating a semiconductor device.

FIGS. 2A to 2E illustrate cross-sectional views of a method forfabricating a semiconductor device in accordance with a first embodimentof the present invention.

FIGS. 3A to 3F illustrate cross-sectional views of a method forfabricating a semiconductor device in accordance with a secondembodiment of the present invention.

FIGS. 4A to 4F illustrate cross-sectional views of a method forfabricating a semiconductor device in accordance with a third embodimentof the present invention.

FIGS. 5A to 5F illustrate cross-sectional views of a method forfabricating a semiconductor device in accordance with a fourthembodiment of the present invention.

DESCRIPTION OF SPECIFIC EMBODIMENTS

Embodiments of the present invention relate to a method for fabricatinga semiconductor device. According to embodiments of present invention,critical dimensions (CD) of a cell region and a peripheral region may becontrolled by additionally performing a simple mask process. Accordingto other embodiments of the present invention, a CD of a P-channelmetal-oxide semiconductor (PMOS) region may be controlled byadditionally performing a simple mask process.

FIGS. 2A to 2E illustrate cross-sectional views of a method forfabricating a semiconductor device in accordance with a first embodimentof the present invention.

Referring to FIG. 2A, an etch target layer 202 is formed over asubstrate 201 including a cell region and a peripheral region. Thesubstrate 201 may include a substrate on which a dynamic random accessmemory (DRAM) process is to be performed. The etch target layer 202includes a conductive layer to be used as a gate electrode or a bit lineelectrode. The etch target layer 202 includes polysilicon, metal, ormetal silicide. The metal may include tungsten, and the metal silicidemay include tungsten silicide.

A hard mask 203 is formed over the etch target layer 202. The hard mask203 includes a nitride-based layer. For instance, the hard mask 203includes a silicon nitride layer.

Mask patterns 204A and 20413 are formed over the hard mask 203. The maskpattern 204A is formed in the cell region and the mask pattern 20413 isformed in the peripheral region. Hereinafter, the mask pattern 204Aformed in the cell region is referred to as the first mask pattern 204Aand the mask pattern 204B formed in the peripheral region is referred toas the second mask pattern 204B. The first and second mask patterns 204Aand 204B are formed to define pattern regions in the cell region and theperipheral region. The first and second mask patterns 204A and 204B mayinclude amorphous carbon. The first and second mask patterns 204A and204B may be formed by: forming an amorphous carbon layer over the hardmask 203; forming a photoresist layer over the amorphous carbon layer;performing a photo-exposure and developing process to pattern and definethe pattern regions; etching the amorphous carbon layer; and removingthe patterned photoresist layer.

Referring to FIG. 2B, the hard mask 203 is etched. Reference numerals203A and 203B refer to a first hard mask pattern 203A remaining in thecell region and a second hard mask pattern 203B remaining in theperipheral region, respectively. At this time, the second hard maskpattern 203B may have a width larger than a desired pattern width due toa loading effect.

A photoresist pattern 205 is formed over the cell region. Thephotoresist pattern 205 may be formed by forming a photoresist layerover the resultant structure, and performing a photo-exposure anddeveloping process to pattern the photoresist layer such that theperipheral region is exposed.

Referring to FIG. 2C, the second hard mask pattern 203B is trimmed. Thetrimming includes performing a plasma etch process. The plasma etchprocess is performed using a gas including tetrafluoromethane (CF₄),fluoroform (CHF₃), and oxygen (O₂).

Accordingly, the first hard mask pattern 203A is protected by thephotoresist pattern 205, and the second hard mask pattern 203B istrimmed to reduce the width. Furthermore, the second mask pattern 204Bformed over the second hard mask pattern 203B reduces damage on an upperportion of the second hard mask pattern 203B while trimming the secondhard mask pattern 203B. Thus, a loss is decreased. Reference numeral203C refers to a trimmed second hard mask 203C in the peripheral region.

Referring to FIG. 2D, the photoresist pattern 205 and the first andsecond mask patterns 204A and 2045 are removed. The photoresist pattern205 and the first and second mask patterns 204A and 204B may be removedat substantially the same time using an oxygen removal process.

Referring to FIG. 2E, the etch target layer 202 is etched to formpatterns. The pattern in the cell region includes a stack structureconfigured with a first etch target pattern 202A and the first hard maskpattern 203A. The pattern in the peripheral region includes a stackstructure configured with a second etch target pattern 202B and thetrimmed second hard mask 203C. The patterns include gate patterns or bitline patterns.

Accordingly, a CD between the cell region and the peripheral region maybe controlled by trimming the second hard mask pattern 203B to reducethe CD, and the trimmed second hard mask 203C may not be formed to awidth that is larger than a desired width, as shown in FIG. 2C.

The first embodiment of the present invention may also be applied to aP-type polysilicon layer in a PMOS region. Hereinafter, a method forfabricating a semiconductor device which can reduce a CD increase of aP-type polysilicon layer in a PMOS region is described in accordancewith following embodiments.

FIGS. 3A to 3F illustrate cross-sectional views of a method forfabricating a semiconductor device in accordance with a secondembodiment of the present invention.

Referring to FIG. 3A, a substrate 301 including an N-channel metal-oxidesemiconductor (NMOS) region and a PMOS region is provided. An N-typepolysilicon layer 302A is formed in the NMOS region, and a P-typepolysilicon layer 302B is formed in the PMOS region. The substrate 301may include a substrate on which a DRAM process is to be performed. TheNMOS region may be an NMOS region of a cell region and a peripheralregion. In the embodiments of the present invention, a cell region isillustrated as the NMOS region.

The N-type polysilicon layer 302A and the P-type polysilicon layer 302Bmay each be formed by implanting N-type or P-type impurities in apolysilicon layer in the NMOS region and the PMOS region. Otherwise, theN-type polysilicon layer 302A and the P-type polysilicon layer 302B maybe directly formed in the NMOS region and the PMOS region, respectively.The N-type impurities may include phosphorus (P) or arsenic (As), andthe P-type impurities may include boron (B).

A metal electrode 303 and a gate hard mask 304 are formed over theN-type polysilicon layer 302A and the P-type polysilicon layer 302B. Themetal electrode 303 may include a stack structure configured with abarrier metal and a metal layer. The metal layer may include tungsten.The gate hard mask 304 includes a nitride-based layer.

All amorphous carbon layer 305, a silicon oxynitride (SiON) layer 306,and a bottom anti-reflective coating (BARC) layer 307 are formed overthe gate hard mask 304. The amorphous carbon layer 305 functions as ahard mask for etching the gate hard mask 304, the SiON layer 306functions as a had mask for etching the amorphous carbon layer 305, andthe BARC layer 307 functions as an anti-reflective coating layer whenforming subsequent first photoresist patterns.

First photoresist patterns 308A and 308B are formed over the BARC layer307. The first photoresist patterns 308A and 3088 define gate patternregions. The first photoresist patterns 308A and 308B are formed byforming a photoresist layer over the BARC layer 307 and performing aphoto-exposure and developing process to pattern and define the gatepattern regions. Hereinafter, the first photoresist pattern 308A formedin the NMOS region is referred to as the first NMOS photoresist pattern308A, and the first photoresist pattern 308B formed in the PMOS regionis referred to as the first PMOS photoresist pattern 308B forconvenience of description. The first NMOS and PMOS photoresist patterns308A and 308B are each formed to have a desired develop inspectioncritical dimension (DICD) in the NMOS region and the PMOS region.

Referring to FIG. 3B, the BARC layer 307, the SiON layer 306, theamorphous carbon layer 305, and the gate hard mask 304 are etched. Atthis time, the first NMOS photoresist pattern 308A, the first PMOSphotoresist pattern 308B, the BARC layer 307, and the SiON layer 306 aresubstantially removed by the time the gate hard mask 304 is etched.Thus, portions of the amorphous carbon layer 305 remain. Hereinafter,the portions of the amorphous carbon layer 305 remaining in the NMOSregion are referred to as a first amorphous carbon pattern 305A, and theportion of the amorphous carbon layer 305 remaining in the PMOS regionis referred to as a second amorphous carbon pattern 305B. Also, portionsof the gate hard mask 304 remaining in the NMOS region are referred toas a first gate hard mask pattern 304A, and a portion of the gate hardmask 304 remaining in the PMOS region is referred to as a second gatehard mask pattern 304B hereinafter.

Referring to FIG. 3C, a second photoresist pattern 309 is formed. Thesecond photoresist pattern 309 exposes the PMOS region. The secondphotoresist pattern 309 may be formed by forming a photoresist layerover the resultant structure, and performing a photo-exposure anddeveloping process. The second photoresist pattern 309 may be formed byperforming a patterning which is substantially the same as the one usedto form masks exposing each of the NMOS and PMOS regions when formingthe N-type polysilicon layer 302A and the P-type polysilicon layer 302B.Accordingly, the second photoresist pattern 309 exposes the PMOS region.

Referring to FIG. 3D, the second gate hard mask pattern 304B is trimmed.The trimming includes performing a plasma etch process using a gasincluding CF₄, CHF₃, and O₂.

At this time, a CD of the second gate hard mask pattern 304B decreasesaccording to an etch time, and the metal electrode 303 is not damageddue to a selectivity. Also, the second amorphous carbon pattern 305Bformed over the second gate hard mask pattern 304B protects an upperportion of the second gate hard mask pattern 304B during the trimming.Thus, a damage generated by the trimming may be decreased. Referencedenotation 304C refers to a trimmed second gate hard mask 304C in thePMOS region.

Referring to FIG. 3E, the second photoresist pattern 309 is removed. Thesecond photoresist pattern 309 may be removed using oxygen plasma. Thefirst and second amorphous carbon patterns 305A and 305B are alsoremoved when the second photoresist pattern 309 is removed.

Referring to FIG. 3F, gate patterns are formed by etching the metalelectrode 303, the N-type polysilicon layer 302A, and the P-typepolysilicon layer 302B, using the first gate hard mask pattern 304A andthe trimmed second gate hard mask 304C. Hereinafter, portions of themetal electrode 303 remaining in the NMOS region are referred to as afirst metal electrode pattern 303A, and a portion of the metal electrode303 remaining in the PMOS region is referred to as a second metalelectrode pattern 303B. Reference numerals 302A1 and 302B1 refer to anN-type polysilicon pattern 302A1 and a P-type polysilicon pattern 302B1,respectively. Even if the P-type polysilicon pattern 302B1 is formedwith a positive slope, a bias increase is not large because the CD isreduced by trimming the second gate hard mask pattern 304B as shown inFIG. 3D.

FIGS. 4A to 4F illustrate cross-sectional views of a method forfabricating a semiconductor device in accordance with a third embodimentof the present invention.

Referring to FIG. 4A, a substrate 401 including an NMOS region and aPMOS region is provided. An N-type polysilicon layer 102A is formed inthe NMOS region, and a P-type polysilicon layer 402B is formed in thePMOS region. The substrate 401 may include a substrate on which a DRAMprocess is to be performed. The NMOS region may be an NMOS region of acell region and a peripheral region. In the embodiments of the presentinvention, a cell region is illustrated as the NMOS region.

The N-type polysilicon layer 402A and the P-type polysilicon layer 402Bmay each be formed by implanting N-type or P-type impurities in apolysilicon layer in the NMOS region and the PMOS region. Otherwise, theN-type polysilicon layer 402A and the P-type polysilicon layer 402B maybe directly formed in the NMOS region and the PMOS region, respectively.The N-type impurities may include P or As, and the P-type impurities mayinclude B.

A metal electrode 403 and a gate hard mask 404 are formed over theN-type polysilicon layer 402A and the P-type polysilicon layer 402B. Themetal electrode 403 may include a stack structure configured with abarrier metal and a metal layer. The metal layer may include tungsten.The gate hard mask 404 includes a nitride-based layer.

An amorphous carbon layer 405, a SiON layer 406, first and secondpatterned buffer layers 407A and 407B, and first and second BARCpatterns 404A and 408B are formed over the gate hard mask 404. In moredetail, a buffer layer and a BARC layer are formed over the SiON layer406. The amorphous carbon layer 405 functions as a hard mask for etchingthe gate hard mask 404, the SiON layer 106 functions as a hard mask foretching the amorphous carbon layer 405, and the BARC layer functions asan anti-reflective coating layer when forming subsequent firstphotoresist patterns. The buffer layer is formed to reduce a CD of thePMOS region during initial processes. The buffer layer includes amaterial having a selectivity to the SiON layer 406. The buffer layerincludes polysilicon, tungsten, or tungsten silicide.

First photoresist patterns 409A and 409B are formed over the BARC layer.The first photoresist patterns 409A and 409B define gate patternregions. The first photoresist patterns 409A and 409B are formed byforming a photoresist layer over the BARC layer and performing aphoto-exposure and developing process to pattern and define the gatepattern regions. Hereinafter, the first photoresist pattern 409A formedin the NMOS region is referred to as the first NMOS photoresist pattern409A and the first photoresist pattern 409B formed in the PMOS region isreferred to as the first PMOS photoresist pattern 409B for convenienceof description. The first NMOS and PMOS photoresist patterns 409A and409B are each formed to have a desired DICD in the NMOS region and thePMOS region.

The BARC layer and the buffer layer are etched to form the first andsecond patterned buffer layers 407A and 407B and the first and secondBARC patterns 408A and 408B. The first patterned buffer layer 407Aformed in the NMOS region and the second patterned buffer layer 4070 isformed in the PMOS region. Also, the first BARC pattern 408A is formedin the NMOS region and the second BARC pattern 408B is formed in thePMOS region. The BARC layer and the buffer layer may be etched using aplasma etch process.

Referring to FIG. 4B, the first NMOS and PMOS photoresist patterns 409Aand 409B and the first and second BARC patterns 408A and 4080 areremoved. The first NMOS and PMOS photoresist patterns 409A and 409B andthe first and second BARC patterns 408A and 408B may be removed usingoxygen plasma. A cleaning process is performed.

A second photoresist pattern 410 is formed. The second photoresistpattern 410 exposes the PMOS region. The second photoresist pattern 410may be formed by forming a photoresist layer over the resultantstructure and performing a photo-exposure and developing process. Thesecond photoresist pattern 410 may be formed by performing a patterningwhich is substantially the same as the one used to form masks exposingeach of the NMOS and PMOS regions when forming the N-type polysiliconlayer 402A and the P-type polysilicon layer 402B. Accordingly, thesecond photoresist pattern 410 exposes the PMOS region.

Referring to FIG. 40, the second patterned but layer 407B is trimmed.The trimming may be performed using a different gas according to thematerial of the second patterned buffer layer 407B. That is, if thesecond patterned buffer layer 407B includes polysilicon, the trimming isperformed using a gas including hydrogen bromide (HBr), chlorine (Cl₂)and O₂. If the second patterned buffer layer 407B includes tungsten ortungsten silicide, the trimming is performed using a gas including Cl₂,nitrogen (N₂), and one of nitrogen trifluoride (NF₃) and sulfurhexafluoride (SF₆).

A CD of the second patterned buffer layer 407B is reduced according toan etch time, and the SiON layer 406 is not damaged due to aselectivity. Reference numeral 407C refers to a trimmed second patternedbuffer layer 407C in the PMOS region.

Referring to FIG. 4D, the second photoresist pattern 410 is removed. Thesecond photoresist pattern 410 may be removed using oxygen plasma. Acleaning process is performed.

Referring to FIG. 4E, the SiON layer 406, the amorphous carbon layer405, and the gate hard mask 404 are etched. The first patterned bufferlayer 407A, the trimmed second patterned buffer layer 407C, and the SiONlayer 406 are removed by the time the gate hard mask 404 is etched.Thus, portions of the amorphous carbon layer 405 remain. Hereinafter,the portions of the amorphous carbon layer 405 remaining in the NMOSregion are referred to as a first amorphous carbon pattern 405A, and theportion of the amorphous carbon layer 405 remaining in the PMOS regionis referred to as a second amorphous carbon pattern 405B. Also, portionsof the gate hard mask 404 remaining in the NMOS region are referred toas a first gate hard mask pattern 404A, and a portion of the gate hardmask 404 remaining in the PMOS region is referred to as a second gatehard mask pattern 404B hereinafter.

Referring to FIG. 4F, the first amorphous carbon pattern 405A and secondamorphous carbon pattern 405B are removed. The first amorphous carbonpattern 405A and second amorphous carbon pattern 405B may be removedusing oxygen plasma. A cleaning process is performed.

The metal electrode 403, the N-type polysilicon layer 402A, and theP-type polysilicon layer 402B are etched to form gate patterns. Portionsof the metal electrode 403 remaining in the NMOS region are referred toas a first metal electrode pattern 403A, and a portion of the metalelectrode 403 remaining in the PMOS region is referred to as a secondmetal electrode pattern 403B. Reference numerals 402A1 and 402B1 referto an N-type polysilicon pattern 402A1 and a P-type polysilicon pattern402B1, respectively. Even if the P-type polysilicon pattern 402B1 isformed with a positive slope, a bias increase is not large because theCD is reduced by trimming the second patterned buffer layer 407B asshown in FIG. 4C.

FIGS. 5A to 5F illustrate cross-sectional views of a method forfabricating a semiconductor device in accordance with a fourthembodiment of the present invention.

Referring to FIG. 5A, a substrate 501 including an NMOS region and aPMOS region is provided. An N-type polysilicon layer 502A is formed inthe NMOS region, and a P-type polysilicon layer 502B is formed in thePMOS region. The substrate 501 may include a substrate on which a DRAMprocess is to be performed. The NMOS region may be an NMOS region of acell region and a peripheral region. In the embodiments of the presentinvention, a cell region is illustrated as the NMOS region.

The N-type polysilicon layer 502A and the P-type polysilicon layer 502Bmay each be formed by implanting N-type or P-type impurities in apolysilicon layer in the NMOS region and the PMOS region. Otherwise, theN-type polysilicon layer 502A and the P-type polysilicon layer 502B maybe directly formed in the NMOS region and the PMOS region, respectively.The N-type impurities may include P or As, and the P-type impurities mayinclude B.

A metal electrode 503 and a gate hard mask 504 are formed over theN-type polysilicon layer 502A and the P-type polysilicon layer 502B. Themetal electrode 503 may include a stack structure configured with abarrier metal and a metal layer. The metal layer may include tungsten.The gate hard mask 504 includes a nitride-based layer.

A buffer layer 505, an amorphous carbon layer 506, a SiON layer 507, anda BARC layer 508 are formed over the gate hard mask 504. The amorphouscarbon layer 506 functions as hard mask for etching the buffet layer505, the SiON layer 507 functions as a hard mask for etching theamorphous carbon layer 506, and the BARC layer 508 functions as ananti-reflective coating layer when forming subsequent first photoresistpatterns.

The buffer layer 505 is formed to reduce a CD of the PMOS region.Forming the buffer layer 505 may reduce a burden of directly trimmingthe gate hard mask 504. The buffer layer 505 includes a material havinga selectivity to the gate hard mask 504. The buffer layer includespolysilicon, tungsten, or tungsten silicide.

First photoresist patterns 509A and 509B are formed over the BARC layer508. The first photoresist patterns 509A and 509B define gate patternregions. The first photoresist patterns 509A and 509B are formed byforming a photoresist layer over the BARC layer 508 and performing aphoto-exposure and developing process to pattern and define the gatepattern regions. Hereinafter, the first photoresist pattern 509A formedin the NMOS region is referred to as the first NMOS photoresist pattern509A and the first photoresist pattern 509B formed in the PMOS region isreferred to as the first PMOS photoresist pattern 509B for convenienceof description. The first NMOS and PMOS photoresist patterns 509A and509B are each formed to have a desired DICD in the NMOS region and thePMOS region.

Referring to FIG. 5B, the BARC layer 508, the SiON layer 507, theamorphous carbon layer 506, and the buffer Layer 505 are etched. At thistime, the first NMOS photoresist pattern 509A, the first PMOSphotoresist pattern 509B, the BARC layer 508, and the SiON layer 507 aresubstantially removed by the time the buffer layer 505 is etched. Thus,portions of the amorphous carbon layer 506 remain. Hereinafter, theportions of the amorphous carbon Layer 506 remaining in the NMOS regionare referred to as a first amorphous carbon pattern 506A, and theportion of the amorphous carbon layer 506 remaining in the PMOS regionis referred to as a second amorphous carbon pattern 506B. Also, portionsof the buffer layer 505 remaining in the NMOS region are referred to asa first buffer pattern 505A, and a portion of the buffer layer 505remaining in the PMOS region is referred to as a second buffer pattern505B hereinafter.

Referring to FIG. 5C, the first and second amorphous carbon patterns506A and 506B are removed. The first and second amorphous carbonpatterns 506A and 506B may be removed using oxygen plasma. A cleaningprocess is performed. A second photoresist pattern 510 is formed. Thesecond photoresist pattern 510 exposes the PMOS region. The secondphotoresist pattern 510 may be formed by forming a photoresist layerover the resultant structure, and performing a photo-exposure anddeveloping process. The second photoresist pattern 510 may be formed byperforming a patterning which is substantially the same as the one usedto form masks exposing each of the NMOS and PMOS regions when formingthe N-type polysilicon layer 502A and the P-type polysilicon layer 502B.Accordingly, the second photoresist pattern 510 exposes the PMOS region.

referring to FIG. 5D, the second buffer pattern 505B is trimmed. Thetrimming may be performed using a different gas according to thematerial of the second buffer pattern 505B. That is, if the secondbuffer pattern 505B includes polysilicon, the trimming is performedusing a gas including HBr, Cl₂ and O₂. If the second buffer pattern 505Bincludes tungsten or tungsten silicide, the trimming is performed usinga gas including Cl₂, N₂, and one of NF₃ and SF₆.

A CD of the second buffer pattern 505B is reduced according to an etchtime, and the gate hard mask 504 is not damaged due to a selectivity.Reference numeral 505C refers to a trimmed second buffer pattern 505C inthe PMOS region.

Referring to FIG. 5E, the second photoresist pattern 510 is removed. Thesecond photoresist pattern 510 may be removed using oxygen plasma. Acleaning process is performed. The gate hard mask 504 is then etched.Reference numerals 504A and 504B refer to a first gate hard mask pattern504A in the NMOS region and a second gate hard mask pattern 504B in thePMOS region, respectively.

Referring to FIG. 5F, the metal electrode 503, the N-type polysiliconlayer 502A, and the P-type polysilicon layer 502B are etched to formgate patterns. Hereinafter, portions of the metal electrode 503remaining in the NMOS region are referred to as a first metal electrodepattern 503A and a portion of the metal electrode 503 remaining in thePMOS region is referred to as a second metal electrode pattern 501B.Reference numerals 502A1 and 502B1 refer to an N-type polysiliconpattern 502A1 and a P-type polysilicon pattern 502B1, respectively.

Even if the P-type polysilicon pattern 502B1 is formed with a positiveslope, a bias increase is not large because the CD is reduced bytrimming the second buffer pattern 505B as shown in FIG. 5D beforeetching the gate hard mask 504.

The first buffer pattern 505A and the trimmed second buffer pattern 505Cmay be removed by the time the gate patterns are formed, or may beremoved after etching the gate hard mask 504 and before etching themetal electrode 503.

In accordance with the embodiments of the present invention, the CD ofthe peripheral region, which increases due to the pattern densitydifference between the cell region and the peripheral region, may becontrolled by additionally forming the photoresist pattern and trimmingthe hard mask in the peripheral region such that the CDs between thecell region and the peripheral region are controlled.

Furthermore, the CD of the PMOS region may be controlled during theformation of the gate patterns in the NMOS and PMOS regions by formingthe photoresist pattern which exposes the PMOS region where the biasincreases due to the P-type polysilicon layer and performing thetrimming process.

Also, the CD of the PMOS region may be sufficiently controlled throughthe simple mask process by trimming the gate hard mask or performing thetrimming process after additionally forming the buffer layer to controlthe CD and form the gate patterns.

Moreover, the bias increase is not large even if the P-type polysiliconlayer in the PMOS region is etched to have positive slope by selectivelycontrolling the CD in the PMOS region.

While the present invention has been described with respect to thespecific embodiments, it wilt be apparent to those skilled in the artthat various changes and modifications may be made without departingfrom the spirit and scope of the invention as defined in the followingclaims.

1. A method for fabricating a semiconductor device, comprising: formingan N-type polysilicon layer and a P-type polysilicon layer over asubstrate including an N-channel metal-oxide semiconductor (NMOS) regionand a P-channel metal-oxide semiconductor (PMOS) region, the N-typepolysilicon layer formed in the NMOS region and the P-type polysiliconlayer formed in the PMOS region; forming a metal electrode layer overthe N-type and P-type polysilicon layers; forming a gate hard mask overthe metal electrode; forming a patterned buffer layer for defining gatepattern regions over the gate hard mask; forming a photoresist patternexposing the PMOS region; trimming the patterned buffer layer in thePMOS region; removing the photoresist pattern; and etching the metalelectrode layer and the N-type and P-type polysilicon layers to formgate patterns using the patterned buffer layer.
 2. The method of claim1, wherein forming the patterned buffer layer for defining the gatepattern regions comprises: forming a buffer layer over the gate hardmask; forming an amorphous carbon layer, a silicon oxynitride (SiON)layer, and an anti-reflective coating layer over the buffer layer;forming a mask pattern for defining the gate pattern regions over theanti-reflective coating layer; etching the anti-reflective coatinglayer, the SiON layer, the amorphous carbon layer, and the buffer layer;and removing the etched amorphous carbon layer.
 3. The method of claim1, further comprising, prior to forming the patterned buffer layer,forming an amorphous carbon layer and a SiON layer.
 4. The method ofclaim 1, wherein forming the patterned buffer layer for defining thegate pattern regions comprises: forming an amorphous carbon layer and aSiON layer over the gate hard mask; forming a buffer layer over the SiONlayer; forming an anti-reflective coating layer over the buffer layer;forming a mask patter for defining the gate pattern regions over theanti-reflective coating layer; and etching the anti-reflective coatinglayer, the buffer layer, the SiON layer, and the amorphous carbon layer.5. The method of claim 2, wherein the buffer layer comprisespolysilicon, tungsten, or tungsten silicide.
 6. The method of claim 4,wherein the buffer layer comprises polysilicon, tungsten, or tungstensilicide.
 7. The method of claim 5, wherein trimming the patternedbuffer layer comprises using a gas including hydrogen bromide (HBr),chlorine (Cl₂) and oxygen (O₂) when the patterned buffer layer comprisespolysilicon.
 8. The method of claim 6, wherein trimming the patternedbuffer layer comprises using a gas including HBr, Cl₂ and O₂ when thepatterned buffer layer comprises polysilicon.
 9. The method of claim 7,wherein trimming the patterned buffer layer comprises using a gasincluding Cl₂, nitrogen (N₂), and one of nitrogen trifluoride (NF₃) andsulfur hexafluoride (SF₆) when the patterned buffer layer comprisestungsten or tungsten silicide.
 10. The method of claim 8, whereintrimming the patterned buffer layer comprises using a gas including Cl₂,N₂, and one of NF₃ and SF₆ when the patterned buffer layer comprisestungsten or tungsten silicide.